This application claims the benefit of Korean Application No. 74181/1997, filed Dec. 26, 1997, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
The present invention relates to an optical disk player, and in particular, to a sync detection device for detecting and generating a sync signal from a signal read from an optical disk.
Known optical disk players includes a sync detection and protection device for detecting a sync signal. The sync detection and protection device minimizes damage to data read from an optical disk.
FIG. 1 is a block diagram of a conventional optical disk player. A pickup 102 reads data recorded on an optical disk 100 and generates an RF (Radio Frequency) signal according thereto. The pickup 102 provides an RF amplifier (RF Amp.) 104 with the RF signal. The RF amplifier 104 amplifies the RF signal and provides the amplified RF signal to a binarizer 106. The binarizer 106 comprises a comparator which converts an RF signal into a string of xe2x80x9c1sxe2x80x9d and xe2x80x9c0sxe2x80x9d based upon a level of the RF signal. The binarizer 106 binarizes the output of the RF amplifier to generate serial binary data (SDATA). The SDATA is output to a sync detection and protection device 110. The sync detection and protection device 110 receives the SDATA and a playback clock signal (PLCK) generated from a voltage controlled oscillator (VCO) 108. The sync detection and protection device 110 detects a sync signal from the SDATA and the PLCK signals, and protects the detected sync signal. In case the sync signal is not detected successfully, the sync detection and protection device 110 inserts a sync signal (i.e., generates a sync insertion signal).
The PLCK signal and SDATA are also applied to a phase detector 112. The phase detector 112 compares a phase of the PLCK signal with a phase of the SDATA to detect a phase difference therebetween. The comparison results, i.e., the detected differences, are fed back to the VCO 108 via a lowpass filter 114. When a defect is detected (by a detect detector not shown), the lowpass filter 114 holds its output value. The VCO 108 generates the playback clock (PLCK) according to the output of the lowpass filter 14, in sync with the data read from the disk 100.
FIG. 2 is a block diagram of the sync detection and protection device 110. The sync detection and protection device 110 includes a sync detector 116 and a sync insertion and protection device 124. The sync detector 116 generally comprises: a register 118; a sync pattern decoder 120; and a sync generator 122. The register 118 generally comprises: a serial-input-parallel-output register. The register 118 receives the SDATA, in series, according to the PLCK, and outputs the loaded binary data (SDATA), in parallel, to the sync pattern decoder 120. The sync pattern decoder 120 checks whether the SDATA coincides with the sync pattern and generates a sync detection signal to the sync generator 122 if the SDATA is coincides with the sync pattern.
The sync insertion and protection device 124 counts the playback clock signal (PLCK), and generates a sync protection window signal to the sync generator 122 when the count value corresponds to a position where the sync signal is to be generated. The sync generator 122 checks whether the sync detection signal is generated during generation of the sync protection window signal. The sync generator 122 outputs a sync detection signal, as the sync signal, if the sync detection signal is generated during generation of the sync protection window signal. However, if the sync detection signal is not generated during generation of the sync protection window signal, the sync generator 122 requests the sync insertion and protection device 124 to generate a sync insertion signal, and outputs the sync insertion signal as the sync signal. After outputting a predetermined number of sync insertion signals, the sync generator 122 resets the sync insertion and protection device 124.
In such a conventional system, after the sync protection window signal is out of sync with the sync detection signal, even though the sync detection signal is generated normally, it is unavoidable that the predetermined number of the insertion sync signals will be generated.
Further, after generation of the predetermined sync insertion signals, the sync protection window is reset according to the sync detection signal. At this moment, sync noises may be unexpectedly generated. If sync noises are generated, the sync protection window is erroneously set, and the subsequently generated normal sync detection signals may be misjudged as erroneous sync detection signals. Based on this misjudgment, the sync insertion and protection device 124 will erroneously generate the predetermined number of the sync insertion signals causing damage to the data.
Finally, when a defect is detected, the lowpass filter 114 holds its output. If the held output value is not coincident with an average value, the playback clock PLCK from the VCO 108 becomes out of sync (shifted), which leads to a shift of the positions where the sync protection window signal and the sync insertion signal are generated.
It is therefore an object of the present invention to provide a sync detection device which stops generating sync insertion signals when a sync detection signal is normally generated after a sync protection window signal goes out of sync with the sync detection signal.
It is another object of the present invention to provide a sync detection device for preventing a sync protection window from being set according to sync noises.
It is still another object of the present invention to provide an optical disk player which prevents a playback clock from being out of sync even when a defect is detected.
According to an aspect of the present invention, a sync detection device for an optical disk player includes a sync detector for detecting a sync signal from a signal read from an optical disk; a sync insertion and protection device for setting a sync protection window according to a sync detection signal from the sync detector in response to a reset signal, counting a playback clock generated from a voltage controlled oscillator to generate a sync protection window signal if the count value is coincident with a position where the sync signal is to be generated, and generating a sync insertion signal in response to a sync insertion request; a sync generator for outputting the sync detection signal if the sync detection signal is in sync with the sync protection window signal, and requesting the sync insertion and protection device to generate the sync insertion signal to output the sync insertion signal if the sync detection signal is out of sync with the sync protection window signal; and a sync noise canceller for counting the playback clock during generation of the sync detection signal, and generating the reset signal to the sync insertion and protection device if the count value reaches a predetermined value.